Usually, in order to acquire a frequency correction burst (FB), a radio communication device opens an acquisition time window during which an RF circuit (radio frequency circuit) is activated in order to receive RF signals. Then, the RF signals received are analyzed in order to locate a frequency correction burst (FB) and compensate for the frequency or time difference.
Usually the acquisition time window is continuous and has a slightly longer duration than the maximum duration between two frequency correction bursts (FB) transmitted successively.
Thus, as illustrated in FIG. 1, in the case of GSM in which a frequency correction burst (FB) is repeated every ten or eleven frames (transmitted in each of the frames numbered 0, 10, 20, 30 and 40, but not in the frame numbered 50, of a multi-frame MF having 51 frames) an acquisition time window 1a, 1b is generally used whose duration is 11.125 frames (that is, eleven frames plus a time slot). FIG. 1 illustrates two examples. In the first example, the acquisition time window 1a begins just after a frequency correction burst (FB) and makes it possible to detect the next frequency correction burst (FB) that is 10 frames from the previous frequency correction burst (FB). In the second example, the acquisition time window 1b begins just after a frequency correction burst (FB) and makes it possible to detect the next frequency correction burst (FB) that is 11 frames from the previous frequency correction burst (FB).
The standard technique therefore includes choosing a continuous acquisition time window whose duration is minimized in order to reduce the acquisition time of a frequency correction burst (FB).
This standard technique is not always optimal, particularly when the radio communication device operates in such a way that at least part of the digital processing means (processor, DSP, etc.) of this radio communication device is deactivated when the acquisition time window is open (that is, when the RF circuit of this same radio communication device is activated), and is activated when the acquisition time window is closed (that is, when the RF circuit is deactivated).
Such an operation involves performing a time domain isolation (TDI) between the RF activities and the digital processing activities. This concept (TDI) is described in further detail below as well as in U.S. patent applications Ser. Nos. 10/955,569, 10/955,584 and 10/954,791. It is intended to improve the performance of the analog RF circuit that is very sensitive to sound and interference. In some applications, the RF circuit must be able to detect very low amplitude signals (a few micro-volts). If the RF circuit is in a noisy environment, it is possible that reception performance will be substantially degraded. Now, the radio communication devices include digital processing circuits, like a digital signal processor (DSP), to find the frequency correction burst (FB) signal, and a microcontroller unit (MCU) to manage all the operations performed by the device. These digital processing circuits generate noise that can interfere significantly with the operation of the RF circuit if it is placed near the digital processing circuits. This is the case, for example, when digital processing circuits and the RF circuit are integrated on one common integrated circuit (also called a chip) or on at least two integrated circuits mounted very close to one another and packaged together (in a multi-chip module (MCM), for example).
One drawback of this time domain isolation technique (TDI) is that the digital processing circuits that are deactivated when the acquisition time window is open cannot support real time applications because they are deactivated for very long periods of time. For example, in the case of GSM, the length of the acquisition time window is 11.125 frames, that is, approximately 55 ms, which is a stop duration that is too long for some digital processing circuits (DSP, processor, etc.) to operate in real time.
The main objective of the disclosed technology is to overcome these various drawbacks of the prior art.
More specifically, one of the objectives of the disclosed technology is to provide a frequency correction burst (FB) acquisition technique using a radio communication device, this technique reducing the duration of each continuous time period for the activation of the RF circuit included in the radio communication device.
Another objective of the disclosed technology, in at least one embodiment, is to provide such a technique which, in the aforementioned context of the time domain isolation technique (TDI), can deactivate for a shorter period of time the digital processing circuits included in the radio communication device, namely those digital processing circuits which are deactivated when the acquisition window is open.
Another objective of the disclosed technology, in at least one embodiment, is to provide such a technique that is simple to implement and inexpensive.
Yet another objective of the disclosed technology, in at least one embodiment, is to provide such a technique that does not significantly modify performance in terms of frequency correction burst (FB) acquisition time.